(1) Field of the Invention
This invention relates to treating fibers used in the manufacture of composites of discontinuous fiber and a polymer matrix and particularly to processes for preparing improved treated cellulose fiber.
(2) Description of the Prior Art
Discontinuous fibers have long been used as fillers or reinforcements for polymer and elastomeric materials. The fibers may be unregenerated cellulose such as cotton or fiberized wood, such as wood pulp, or fiberized synthetic filaments such as nylon, aramid, polyester or glass. Cellulosic or synthetic fibers have not only been used as fillers, but they have also been used as reinforcements in rubber articles such as tires, hose and power transmission belts. As particularly discussed in U.S. Pat. Nos. 3,697,364 and 3,709,845, it is very difficult to mix fibers into massed rubber with good dispersion because the fibers tend to cling together in bundles or prills rather than being homogeneously dispersed into the rubber.
The above cited references teach improvements for dispersing and bonding discontinuous cellulosic fibers, or mixtures thereof, in a viscoelastomeric matrix to yield a vulcanized composite with increased Young's modulus. As taught thereby, fiber dispersity in rubber is enhanced by a process that involves slurrying pulped and dried fibers in water at about 2% consistency, adding liquid latex, and coagulating the latex on the fibers. The coagulation is filtered and dried leaving "pellets" or "curd" agglomerations of latex encapsulating and bonding together clusters of unoriented fibers. The object of the latex coating on the fiber clusters is to reduce fiber-to-fiber interactions and fiber breakage when the pellets are dispersed in a viscoelastomer with an intensive mixing means such as a cold-feed extruder, Banbury mixer or mill. Alternatively, carbon black may be added to the slurried fiber as a partitioning agent to reduce fiber-fiber interaction.
U.S. Pat. No. 3,836,412 also teaches treating cellulose fibers with elastomer in an aqueous slurry to improve the properties of later formed vulcanizable elastomer-treated fiber composite. The fiber treatment is taught to occur in aqueous slurries of from 1.66 to 2% consistencies formed by slurrying pulped and dried wrapping paper fibers.
U.S. Pat. No. 3,943,079 teaches pretreating unregenerated cellulose fibers prior to their dispersion in a polymer matrix by mixing minor proportions of a plastic polymer and a lubricant with the fiber under shearing forces. The required amount of plastic polymer is taught to depend on the type and amount of lubricant.
The present invention simplifies the preparation of treated fiber and provides an improved polymer treated fiber which evenly disperses in an elastomeric matrix quickly and provides an improved composite.